In recent years, a radiographic image conversion panel in which a stimulable phosphor substance is formed on a support is utilized for recording radiographic images. In this method, a portion of the radiation transmitted through a subject for image taking is absorbed by a stimulable phosphor substance layer formed on a radiographic image conversion panel. Thereafter, excitation light such as laser light is irradiated on the stimulable phosphor layer to make radiation energy accumulated in a stimulable phosphor layer emit as phosphor light which is detected, resulting in formation of images.
As a method to form a stimulable phosphor substance layer on such a radiographic image conversion panel, there is known a method in which a binder is mixed with a stimulable phosphor substance and the resulting mixture is coated on a support. However, this method may lower the purity of a stimulable phosphor substance causing decreasing the efficiency of excitation light penetration and stimulated emission, and resulting in deterioration of image qualities such as sharpness and granularity of recorded images. Therefore, a method to form a stimulable phosphor substance layer by means of a vapor-accumulating method (or a gas phase accumulation method) has been developed to improve image quality of recorded images (for example, refer to a Patent Literature 1). In this method, since a stimulable phosphor substance layer contains only a stimulable phosphor substance without a binder, the efficiency of excitation light penetration and stimulated emission is improved resulting in obtaining images of high quality.
A conventional manufacturing method of a radiograph image conversion panel by a vapor-accumulating method will be now explained referring to FIG. 4.
In a vapor-accumulating method, a stimulable phosphor substance is accumulated on a support by means of evaporation or sputtering, and, for example, evaporation system 10 shown in FIG. 4 has been utilized in case of an evaporation method. Evaporation system 10 contains vacuum chamber 12 equipped with vacuum pump 11, vapor source 13, and support transporting mechanism 14 which supports support S as well as transports support S back and forth against vapor source 13 in the horizontal direction in said vacuum chamber 12. Further, in this evaporation system 10, slit plate 15 is installed between vapor source 13 and support S to restrict evaporation onto support S, while transferring support S.
In this evaporation system 10, a stimulable phosphor substance layer can be formed nearly uniformly onto all over support S by evaporating vapor of a stimulable phosphor substance which has passed through slit 15 from vapor source onto support S.
A radiographic image conversion panel utilized in this radiographic image recording and reproducing method contains a support and a stimulable phosphor substance layer provided on the support. As a stimulable phosphor substance, utilized is one which comprises an alkali halide such as CsBr as a mother substance being activated with Eu, and it is considered that an X-ray conversion efficiency can be improved, which has been impossible heretofore, specifically by employing Eu as an activator.
Further, there is a correlation between the concentration of an activator and the luminance, and the higher is the concentration of an activator, the higher is the sensitivity. And the sensitivity is saturated at the limiting concentration of an activator at which excitation light can penetrate into the phosphor substance layer and make the accumulated energy to release at the time of reading. Therefore, the more non-uniform is the concentration of an activator, the more uneven is the sensitivity.
Therefore, by making the concentrations of an activator (a mol ratio of an activator to a mother substance) of arbitrary two points in a phosphor substance layer into a predetermined range, developed has been a radiographic image conversion panel which has an improved sensitivity as well as can provide radiographic images of high image quality (refer to patent literature 2).
[Patent Literature 1] Japanese Patent Publication Open to Public Inspection (JP-A) No. 2002-214397.
[Patent Literature 2] JP-A No. 2003-28994